This invention relates generally to apparatus and methods for perforating wells, especially oil or gas wells. The invention more particularly relates to such apparatus and methods in which multiple perforating gun sections are put in the well at one time and released to fall to the bottom of the well after the perforating operation. In its preferred implementation, the invention incorporates a longitudinally deformable or flexible unitary member.
In completing an oil or gas well, a perforation operation is frequently used to open passageways for oil or gas in a subterranean formation or zone to flow into the borehole and up to the surface. Explosive charges are detonated to generate high pressure jets that create the perforations.
Tubing conveyed perforating systems to accomplish the foregoing can be conveyed into wells on a tubing or pipe string with the string left in position in the well during the perforating of the well. Such systems include one or more devices which carry the explosive charges. These devices are referred to as perforating guns. After perforating the well, the perforating guns may have disintegrated or may be retrieved, or they may be released or dropped from the tubing or pipe string through the use of various techniques.
One such technique is an automatically releasing gun hanger which has been proposed as shown in U.S. Pat. No. 5,156,213 to George et al. The George et al. '213 patent describes an automatically releasing gun hanger which is run into the well on a rigid tubing string or pipe string. The gun hanger is set within the well by a rotating motion of the rigid tubing string or pipe string. Through further rotational motion, the rigid tubing string or pipe string is then disconnected from the perforating gun attached to the gun hanger. The tubing or pipe string can then be removed from the well. The perforating gun is fired by a pressure actuated firing head. Upon firing of the perforating gun, the gun hanger automatically releases, thus allowing the gun to drop to the bottom of the well.
It has also been proposed to run the perforating gun into the well on a coiled tubing string. In such cases, rotation of the string as with a rigid tubing string or pipe string is not possible. U.S. Pat. No. 5,398,760 to George et al. discloses a modified version of the apparatus shown in the George et al. '213 patent. In this modified version, the actuating mechanism of the gun hanger is such that it is operated by a simple reciprocating motion of the coiled tubing string without the need for any rotating motion. Also, a pressure responsive release mechanism connects the coiled tubing string to the perforating gun so that after the gun hanger is set within the casing, pressure within the coiled tubing string may be increased to release the coiled tubing string from the perforating gun, thus allowing the coiled tubing string to be retrieved prior to firing the perforating gun.
While both of the previously described apparatus work well, in some situations problems may occur. For example, when there is an insufficient "rathole" in the bottom of the well into which to drop the entire perforating gun assembly, a portion of the gun assembly may interfere with flow of fluids from the perforated formation. The potential for this problem may be especially present with perforating systems using longitudinally spaced perforating gun sections such as described in U.S. Pat. No. 4,612,992 to Vann et al. and U.S. Pat. No. 4,619,333 to George. One possible solution to this is to provide selectably retrievable gun sections. U.S. Pat. No. 5,366,014 to George describes a modular gun system in which only the sections that remain across the perforations after firing need to be retrieved.
To avoid the need to retrieve gun sections, which can be time consuming and costly, preferably the portion released to the bottom of the well can be collapsed such that it does not interfere with the perforations even when there is limited rathole height below the perforations. Proposals for this type of solution are set forth in U.S. Pat. No. 4,790,383 to Savage et al. and U.S. Pat. No. 4,905,759 to Wesson et al. These patents disclose multiple-component, operating mechanical structures which undergo telescoping movement of one portion relative to another portion. It would be desirable if a simpler interconnecting structure could be provided to avoid shortcomings which might exist with such a multi-component, telescoping movement structure. A simpler, less complicated structure should result in fewer failures and thus be more reliable. Such a simple structure should also preferably better accommodate shallower ratholes by providing a shorter collapsed profile than a multi-component, telescoping structure.